Video compression standards, such as MPEG-2 and H.264 (also known as MPEG-4, Part 10, and Advanced Video Coding), allow current cable and satellite television services to provide over 100 channels of television content. Each channel can be associated with video, audio, as well as textual data. The video data and audio data are compressed and encoded as elementary streams. The elementary streams are packetized and multiplexed with elementary streams associated with other channels over a transmission media.
At the decoder, the decoder decodes the elementary streams associated with the channel(s) that the viewer is viewing. When the viewer switches to a new channel, the decoder decodes the elementary streams associated with the channel.
However, there is usually a delay between the time the user switches channels and the time that the decoder provides decoded pictures from the new channel. There are several reasons for this.
One reason for this is that many decoder systems have buffers, queues, and pipelines for decoding the video data. The decoder generally buffers portions of the video elementary stream prior to decoding the portions. Additionally, the decoder decodes portions of the video elementary stream in stages. Each stage simultaneously decodes different portions of the video elementary stream. Decoder systems can also use a queue for providing pictures for display.
When a channel change occurs, the buffer, pipeline, and queue are still filled with portions of the video elementary stream of the previous channel. The decoder system discards the foregoing, and portions of the video elementary stream associated with the new channel proceed through the buffer, pipeline, and queue. There is a time lag for the portions of the video elementary stream associated with the new channel to proceed to display.
Another reason for this delay is that the decoder waits for a sequence header. The video elementary stream comprises at least one video sequence. The video sequence further comprises what are known as sequence headers. The sequence headers include data that the decoder uses for decoding. This data specifies the vertical and horizontal size of the picture, the aspect ratio, pixel sub-sampling format, the picture rate, the use of progressive scan or interlace scan, the profile, level, and bit rate, and quantizing matrices used in intra and inter-coded pictures. The sequencer headers are at certain intervals within the video elementary stream. At the moment of the channel change, the decoder waits until receiving a sequence header from the video elementary stream associated with the new channel.
Another reason for the delay is to achieve time synchronization. The pictures in a video elementary stream include time stamps, indicating when the picture is to be displayed. The decoder uses the time stamps to display the pictures in the correct order, and at the correct times. When the decoder system displays a video elementary stream associated with one channel, the decoder system synchronizes to a time base associated with the video elementary stream. During a channel change, the decoder system synchronizes to a time base associated with another video elementary stream. This adds an additional delay to the time when the user changes the channel to the time the decoder system displays the video from the new channel.
During the time starting from when the user changes the channel and the time that the display provides video from the new channel, the display projects an empty screen. Although this time period is usually short, the viewer often does notice the blank screen. The blank screen becomes more noticeable when the viewer engages in what is known as “channel surfing”. During channel surfing, the viewer changes to a channel, quickly glances at what is shown, and proceeds to the next channel, until the viewer selects a channel to watch.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.